It was my understanding that all of the Lugers were kit boats. Consequently, the owner could have built the boat with a fin keel. Interesting to see how the hull is strengthened to support the weight and side loading of the keel. The original specs were to lay down foam half tubes and glass over them to make an internal grid. Then the interior was added for more structure. Certainly an interesting boat. You might look on the MacGreggor web site. There is a guy in Southern Ca who has an early prototype that is fitted with a fin. He might be of some help when you get to the point of tuning. The boats are quite similar. Good Luck.